The invention relates to a method for controlling the tension between the roll stands of mill trains for steel bars, wires or profiles by controlling the rotational speed of the driving mechanisms of consecutive roll stands.
Tensile and compressive forces affect the tolerances of the dimensions of the cross-section of rolling stock billets, as well as the uniformity of the course of the rolling process itself. An effective control of tension, by means of which, in particular, the build-up of compression in the rolling stock in the longitudinal direction is prevented, is therefore of great importance. Various methods of controlling the tension in the rolling plants have become known in the art. One method consists of calculating the quotient of rolling moment to rolling force and drawing a conclusion from this quotient concerning the tension existing in the rolling stock. Furthermore, a lead method is known, for which the speed differences between the rolling stock billets of consecutive supporting frameworks are evaluated. Additionally, loop controls are known, for which the height of the loop is a measure of the tension or compression in the rolling stock.
It is also known (German Offenlegungsschrift 1 602 020) that, in the case of two consecutive roll stands, values equivalent to the tension, such as the load current of the driving mechanism of roll stands, may be determined and compared with an empirical value and the thereby resulting deviations used for controlling the regulating and controlling devices of the driving mechanism of the subsequent, second roll stand. In a different method (DE 4 220 121), which works with only one comparison value and takes into consideration only one point of the load current profile of the driving mechanism of the roll stand, changes in the temperature structure cannot be detected over the length of the rolling stock and can therefore not be used for control purposes. A different proposal (German Offenlegungsschrift 2 448 033 and German patent 38 06 063) of using, as a regulating variable, the ratio of the armature current of the driving mechanism to the roll separating force, which results from the deformation in the roll gap and which is determined with the aid of load cells installed in the roll stand, did not gain acceptance in practice. This lack of acceptance is because the arrangement and reliability of the pressure measuring devices, especially their maintenance, was associated with difficulties, which have so far not been eliminated. A proposal to determine the load current of the downstream equipment and comparing it in each case with the determined and stored values from preceding supporting frameworks and forming a relative comparison value for control corrections also did not gain acceptance in practice.
It is an object of the invention to improve the generic method so that the tension control between the supporting frameworks of the mill train can be achieved with the help of simple, conventional commercial measurement and control devices disposed outside of the supporting framework.
This objective is accomplished due to the fact that, at least one characteristic of the oscillations, which the rod or wire carries out between two consecutive roll stands, is determined quantitatively and, by comparison with identification points of the oscillations, a tension or compression, existing in the rolling stock between the supporting frameworks, is determined and one of the roll stands is readjusted so that the desired tension builds up in the rolling stock between the roll stands.
As furthermore provided by the invention, an oscillation-determining device for the quantitative determination of at least one characteristic property of an oscillation of the rolling stock may be disposed between the roll stands transversely to a transporting device from the front to the rear roll stand and this detection device may be connected with a tension-determining device, by means of which a tension or compression, existing in the rolling stock between the roll stands, can be determined by a comparison of oscillation identification points.
The characteristic property of the oscillation may be the frequency and/or the amplitude of the oscillation. The readjustment of the roll stand can be accomplished, for example, by providing the readjusted roll stand with an additional desired rotational speed value (i.e., rpm) based on a difference between the existing tension or compression and the desired tension or compression.
If the characteristic property of the oscillation is determined by means of a camera device, which supplies at least one unidimensional dynamic image of the rolling stock transverse to the transporting device, then the determination of the characteristic property is particularly simple.
If the camera device supplies at least two, unidimensional dynamic images of the rolling stock transverse to the transporting device, wherein the images are recorded from different directions, then the oscillation can be determined independently of its plane of oscillation. A variation of the plane of oscillation may arise, particularly, in the case of rod-shaped rolling stock.
If, by means of the dynamic images, at least one dimension of the rolling stock is determined transversely to the transporting direction, an even better determination of the tension or compression, existing in the rolling stock between the roll stands is possible. Moreover, it is possible that, because of the fixed dimensions of the rolling stock, at least one control parameter of the front roll stand, especially a value or a roll gap value, is varied. In the case of rod-shaped rolling stock, the fixed dimension, preferably, is the width of the profile, since the width is more sensitive to tension than the height of the profile.
The camera device can more easily be moved out of the mill train if the camera device is disposed in a frame that can be moved as a unit.
The camera device can be operated more reliably if the frame is closed and there is excess pressure in its interior and the interior is.
Although the oscillation identification points can be determined theoretically, a gradual self-calibration is preferred.
The rolling stock has a point. The self-calibration therefore can take place, for example, due to the fact that
after the point the rolling stock has entered the front roll stand and before it enters the rear roll stand, a front free moment, applied by the front roll stand, is determined,
after the point of the rolling stock has entered the rear roll stand, a front tensile moment, applied by the front roll stand, is determined,
a tension, existing in the rolling stock, is determined from a comparison of the front free moment and the front tensile moment and
the tension and the characteristic property of the oscillation, measured at this tension, are stored as an identification point in a memory.
The rolling stock also has an end. The self-calibration can therefore also be accomplished due to the fact that
after the rolling stock runs out of the supporting framework immediately ahead of the front roll stand and before it runs out of the front framework, a rear tensile moment, applied by the rear roll stand, is determined,
after the end of the rolling stock runs out of the front roll stand, a rear free moment, applied by the rear roll stand, is determined,
from a comparison of the rear free moment and the rear tensile moment, a tension, existing in the rolling stock, is determined and
the tension and the characteristic property of the oscillation, measured at this tension, are stored as identification point in a memory.
If additionally a temperature, existing in the rolling stock, is also determined and stored, complete reproducible information concerning the identification point, related to the quality of the rolling stock, is available.
When rolling profiled rods, the invention makes provisions so that, between two consecutive supporting frameworks, the profile of the rod is measured with profile meters and the values of the respective flange widths, determined by these measurements, are compared in a computer with specified fixed values, for correcting the rpm regulating values of the subsequent supporting frameworks. The values of the flange width, determined by the profile meters, can be compared with values of flange widths, which were determined by further profile meters, upstream from the two roll stands. At the same time, the flange width of laser measuring equipment or line cameras, which determine profiles, can also be used.
Furthermore, when the measurement equipment is disposed in a compact roller group, consisting of a universal supporting framework at the inlet, an intermediate edger and a universal supporting framework at the outlet, a first measurement of the flange width of the rolling stock billet, entering the compact roller group, can be carried out between the universal supporting framework on the inlet side and the intermediate edger, before this profiled billet reaches the universal framework on the outlet side. This is then followed by a second measurement, when the universal supporting framework at the outlet side has taken hold of the profiled billet.
This procedure makes use of the changes in the dimensions of the cross section of the profile, which result from the tension acting on the profiled rod between the two roll stands. This change occurs particularly in the flange width of girders and similar profiles and can easily be accurately determined with the means given.